This project will compare the effects of partial joint deafferentation with the effects of total limb deafferentation on otherwise normal dog knee joints. It is assumed that small articular nerves supplying these joints transmit sensory impulses centrally that are there translated into protective muscular reflexes. Diminishing this sensory input by cutting articular nerves, and abolishing such input by dorsal rhizotomy, should lead to increased microtrauma to articular and periarticular tissues resulting in osteoarthritis (neuropathic arthropathies). Partial joint deafferentation should lead to lesions qualitatively similar to, but of lesser severity and later onset than, those arising from dorsal rhizotomy. Articular cartilage will be evaluated biochemically (Dr. Kenneth Brandt, this school, has agreed to continue collaboration), histochemically, and according to gross pathological criteria. Articular nerves will be characterized by electron microscopy, and periarticular tissues studied by light microscopy, to associate specific axon diameters and nerve ending types with lesions. Pilot studies in collaboration with Dr. Brandt on the dog model revealed biochemical changes of articular cartilage as early as 3 weeks after surgery to cut posterior and medial articular nerves that were more pronounced at 9 weeks after surgery. These changes are specific to the earliest known changes of osteoarthritis. Articular nerves were characterized and nerve endings identified. This project is conceptually unique: it views synovial joints as sensory mechanisms, and suggests that a joint's mechanical integrity may depend upon the integrity of that joint's sensory supply. Positive results will suggest the advisability of reevaluating approaches to synovial joints used in orthopedic surgery taking into account the course, size, distribution, composition, and reflex effects of articular nerves. Perhaps more importantly, positive results will raise the question as to whether so-called "primary osteoarthritis" (that arising spontaneously, usually in older individuals) may actually be secondary to some heretofore unsuspected peripheral or central nervous system disorder.